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<title>Dynamic buffer requirements</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.DynamicBuffer"></a><a class="link" href="DynamicBuffer.html" title="Dynamic buffer requirements">Dynamic buffer requirements</a>
</h3></div></div></div>
<p>
A dynamic buffer encapsulates memory storage that may be automatically resized
as required, where the memory is divided into an input sequence followed
by an output sequence. These memory regions are internal to the dynamic buffer
sequence, but direct access to the elements is provided to permit them to
be efficiently used with I/O operations, such as the <code class="computeroutput">send</code> or
<code class="computeroutput">receive</code> operations of a socket. Data written to the output sequence
of a dynamic buffer sequence object is appended to the input sequence of
the same object.
</p>
<p>
A dynamic buffer type <code class="computeroutput">X</code> shall satisfy the requirements of <code class="computeroutput">MoveConstructible</code>
(C++ Std, [moveconstructible]) types in addition to those listed below.
</p>
<p>
In the table below, <code class="computeroutput">X</code> denotes a dynamic buffer class, <code class="computeroutput">x</code>
denotes a value of type <code class="computeroutput">X&</code>, <code class="computeroutput">x1</code> denotes values
of type <code class="computeroutput">const X&</code>, and <code class="computeroutput">n</code> denotes a value of
type <code class="computeroutput">size_t</code>, and <code class="computeroutput">u</code> denotes an identifier.
</p>
<div class="table">
<a name="boost_asio.reference.DynamicBuffer.t0"></a><p class="title"><b>Table 9. DynamicBuffer requirements</b></p>
<div class="table-contents"><table class="table" summary="DynamicBuffer requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
expression
</p>
</th>
<th>
<p>
type
</p>
</th>
<th>
<p>
assertion/note<br> pre/post-conditions
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput">X::const_buffers_type</code>
</p>
</td>
<td>
<p>
type meeting <a class="link" href="ConstBufferSequence.html" title="Constant buffer sequence requirements">ConstBufferSequence</a>
requirements.
</p>
</td>
<td>
<p>
This type represents the memory associated with the input sequence.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">X::mutable_buffers_type</code>
</p>
</td>
<td>
<p>
type meeting <a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">MutableBufferSequence</a>
requirements.
</p>
</td>
<td>
<p>
This type represents the memory associated with the output sequence.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x1.size()</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">size_t</code>
</p>
</td>
<td>
<p>
Returns the size, in bytes, of the input sequence.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x1.max_size()</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">size_t</code>
</p>
</td>
<td>
<p>
Returns the permitted maximum of the sum of the sizes of the input
sequence and output sequence.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x1.capacity()</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">size_t</code>
</p>
</td>
<td>
<p>
Returns the maximum sum of the sizes of the input sequence and
output sequence that the dynamic buffer can hold without requiring
reallocation.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x1.data()</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">X::const_buffers_type</code>
</p>
</td>
<td>
<p>
Returns a constant buffer sequence <code class="computeroutput">u</code> that represents
the memory associated with the input sequence, and where <code class="computeroutput">buffer_size(u)
== size()</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x.prepare(n)</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">X::mutable_buffers_type</code>
</p>
</td>
<td>
<p>
Requires: <code class="computeroutput">size() + n <= max_size()</code>.<br> <br>
Returns a mutable buffer sequence <code class="computeroutput">u</code> representing the
output sequence, and where <code class="computeroutput">buffer_size(u) == n</code>. The
dynamic buffer reallocates memory as required. All constant or
mutable buffer sequences previously obtained using <code class="computeroutput">data()</code>
or <code class="computeroutput">prepare()</code> are invalidated.<br> <br> Throws:
<code class="computeroutput">length_error</code> if <code class="computeroutput">size() + n > max_size()</code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x.commit(n)</code>
</p>
</td>
<td>
</td>
<td>
<p>
Appends <code class="computeroutput">n</code> bytes from the start of the output sequence
to the end of the input sequence. The remainder of the output sequence
is discarded. If <code class="computeroutput">n</code> is greater than the size of the
output sequence, the entire output sequence is appended to the
input sequence. All constant or mutable buffer sequences previously
obtained using <code class="computeroutput">data()</code> or <code class="computeroutput">prepare()</code> are
invalidated.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">x.consume(n)</code>
</p>
</td>
<td>
</td>
<td>
<p>
Removes <code class="computeroutput">n</code> bytes from beginning of the input sequence.
If <code class="computeroutput">n</code> is greater than the size of the input sequence,
the entire input sequence is removed. All constant or mutable buffer
sequences previously obtained using <code class="computeroutput">data()</code> or <code class="computeroutput">prepare()</code>
are invalidated.
</p>
</td>
</tr>
</tbody>
</table></div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2018 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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